Electric amplification of sounds



22, 1933- .J. KRE-SSMANN 1,923,870 I ELECTRIC AMPLIFICATION OF SOUNDSFiled March 6, 1950 3 Sheets-Sheet l M/ vEN oR 'ATT KN E75.

Aug. 22, 1933. ,J KRESSMANN 1,923,870

ELECTRIC AMPLIFICATION OF' SOUNDS Filed March 6, 1930 3 Sheets-Sheet 2 N/VTaR ATTORNEYS.

Aug. 22, 1933. J. KRESSMANN 119239879 ELECTRIC AMPLIFICATION OF SOUNDSFiled March 6, 1950 3 Sheets-Sheet 5 Patented Aug. 22, 1933 ELECTRICAMPLIFICATIQN F SOUNDS Jean Kressmann, Bordeaux, France ApplicationMarch 6, 1930, Serial No. 433,573, and in France January 24, 1930 4Claims. (01. 181-31) It is known that unlike musical brass instrumentssuch as trumpets, cornet-a-pistons etc. which emit simple sounds whichhave no harmonics, or very little, musical wood instruments 5 (violins,cellos, pianos, harps, clarinets, hautboys etc.) emit sounds which owingto the resonance of the thin and sonorous wood surfaces with whichtheyare provided and which in certain of the said instruments constitutewhat is called the sound board, comprise a very large number ofharmonics which may be called wood harmonics. These harmonics prolong ina way the initial sound, owing to which these instru ments are given atimbre quite difiercnt from that of brass instruments. 1

Thus when one of the hammers of a piano for instance strikes its string,it produces an initial sound, the vibrations of which are prolonged bythe sound board'of the piano (wood harmonics) When however the soundsproduced by the musical instruments are recorded and then reproducedwith electric amplification with the assistance of the apparatus now inexistence,

it is found that the loud speakers utilized (electrodynamic loudspeakers) though they emit completely or practically completely thevibrations produced by the brass instruments, do not transmit, ortransmit only to a very slight extent, the vibrations due to theharmonics of the wood in wood instruments- The timbres of the sounds ofdifferent instruments thus recorded, reproduced and amplified, havetherefore a tendency to resemble each other, owing to the absence of thesaid wood harmonics in the reproduction.

It has been attempted in the present invention to remedy thesaid-drawbacks, and it has been found that after a large number ofexperi- 40 ments with anelectrodynamic loud speaker of any desiredwell-known type, it was possible to get with great exactitude thespecial timbre of wood instruments, that is to say to reconstitute thewood harmonics which strike the human ear perceiving the sounds emittedby the said instruments. It is sufficient for the purpose in question tocombine the loud speaker with a resonance box or sound box comprisingone or more sound board or sonorous surfaces which become operativeunder the action of the vibrations transmitted by the sound wavesescaping from the loud speaker, to the air in the box so as to producewood harmonics.

If we take for instance apiano, the sounds of which are assumed to berecorded by a micro li,-however, the loud speaker which'amplifies thesaid sounds, is combined with a sound resonance box according to theinvention, the son rous surface or surfaces or" the said box (iorming inreality sound boards), impressed by the vibrations imparted to the massoi" air in the box by the sound waves emitted by the loud speaker (andcorresponding to the sounds and to the initial harmonics of the piano,which a'ione are recorded), will produce complementary harmonics or woodharmonics practically in the same conditions in which the said har 7-5monies had been produced in the piano.

Onthe contrary, it with thesame loud speaker combined with a sound boxare reproduced the sounds of a trumpet for instance (sounds which in thetrumpet itself are accompanied 89 only by rare harmonics), the soundboardor boards of the box will remain silent, as the sounds in questioncannot produce wood harmonies,

As another characteristicof the invention, it has been found that thesonority of the sound board or boards of the said resonance box combinedwith the loud speaker, could bematerially increased by stretching one ormore strings either between the said boards or on the said, boards,preferablywith the interposie tion in the latter case of a bridge.

t goes without saying that the present ll}- vention is applicable toelectromagnetic loud speakers in general, whether these latter be usedfor amplifying the sounds transmitted by a gramophone' or by a wirelesstelephony apparatus. I

The accompanying drawings show diagrammatically by way of non-limitativeexamples, various constructions of devices enabling the object of thepresent invention to be achieved.

In the said drawings:

Figure l is a vertical section of a first cone struction and 1 Figure 2is a view in planof the sound board.

Figure 3 isa section of a modified construc-' tion,

Figure 4 is a section of a further modified 001'1', struction and Figure5 is a front elevation of the sound screen.

Figure 6 is a detail View.

In Figures 1 and 2, 1 is a cabinet, preferably of wood, in the interiorof which is arranged an electrodynamic loud speaker 2, or" any desiredwell-known type.

At right angles to the axis of the said loud speaker, that is to say tothe direction of the sound. waves which it emits, is arranged, in

I contact with the horn 3 of the loud speaker,

a screen 4 secured to a cross bar 5 mounted between the walls of thecabinet 1. The screen 4, provided opposite'the horn 3 with an openingfor the propagation of the sound waves, prevents the latter from comingback and striling the horn from the back, which would result ininterferences injurious to the quality and to the good progression ofthe sounds. In Figure 1, the said screen is inclined to the extent ofabout 20 relatively to the vertical, for the reason set forth in thefollowing.

At the upper part of the cabinet and above or in the cover 6 of the sameis arranged a sound board constituted by a frame '7 supporting forinstance a sonorous wood plate 8 of small thickness. Strings 9, thenumber of which is variable at will (seven in the example illustrated),are stretched above the sound board thus constituted, to the frame ofwhich they are securedby means of turn-buckles or strainers 10 of anywell known type. lhese strings pass over a bridge 11 for instance ofwood of curved shape so as to divide the strings in 35' question intosections of a length gradually increasing at one side and decreasing atthe other. 7

With this arrangement, the cabinet 1, closed in front by a stretchedcloth 26 and at the back for instance by a netting 2'7, forms aresonance box, and the no es of air which it contains, is set vibratingunder the action of the sound waves emitted by the loud speaker. These,vibrations of the mass of air of the cabinet are transmitted to thesonorous plate 8, the sonority of which is very considerably increasedby the use of the stretched cords 9.

The inclination of the screen 4 relatively to the vertical and to thesound board 78, is required in order to prevent the latter from beingwithin the minimum field of action of the waves emitted.

In the modified construction of Figure 3, the sound board 7-8 isreplaced by a simple sonorcus plate 12 mounted for instance in a frame13 and forming a cover of the cabinet 1. .Cords 14 are stretchedby-means of strainers 15 between the said plate and the bottom 16 forthe cabinet which may also be made from sonorous wood.

The vibrations of the mass of air enclosed in the cabinet, aretransmitted to the sonorous plate 12 and eventually to the sonorousbottom 16, the sonority of which is increased owing to the use of thestretched strings 14.

In the modified construction shown in Figures 4 and 5, the sound boardisconstituted by the screen 4 itself which may be formed then, like thesound board of Figures 1 and 2, by a frame 17 supporting a sonorousboard 18 provided then with an opening 19 in front of the loud speaker2. Strings 20 are stretched as before on the frame 17 by means ofstrainers 21 and pass over a bridge 22.

In such a case, the loud speaker may be with horizontal axis or not, thescreen 4 being therefore vertical or inclined, but always in thoroughcontact with the horn 3.

In the upper part of the cabinet may be arranged the trap cover 23supporting the rotary disc 24 of a gramophone.

The vibrations of the mass of air enclosed in the cabinet 1 aretransmitted to the sonorous board'l8, the sonority of which is increasedby the st 'ings 20.

In these various figures, the loud speaker 2 may be secured directly onthe screen 4 by means of ties 25.

Instead of providing in Figure 1 only one sound board 789 on one of thewalls of the cabinet 1, other similar ones could be provided onother'walls of the cabinet, the frames 7 of these sound boards beingconnected to the walls in question by cross-barakeys or other suitabledevices.

Finally each sound board could comprise a single sonorous plate (likethe plate 8 of Figure 1) or two plates 8 and 8 as in Figure 6 forinstance at either side of theirame I claim: 1. In a mechanism for theelectric amplifica tion of sounds by means of electro-dynamic loudspeaker, a box for said loud speaker, a light screen dividing said boxinto two compartments and supporting said loud-speaker in said sound boxin a manner to allow free vibration of the cone of saidloud speaker.

2. In a mechanism for the electric amplifi. cation of sounds by means ofelectro-dynamic loud-speaker, the combination with an electric dynamicloud speaker, of a sound box for said loud speaker, at frai e memberforming a wall of said box, a vibratoryplate secured to said framemember, a light screen supporting said loudspeaker in amanner to allowthe'free vibration or the cone of said loud speaker, said screenallowing the waves to reach said plate and at the same time interruptingpassage of the sound waves to the rear thereof thereby preventinginterference with subsequently produced sounds.

3. In a mechanism for the electric amplification of sounds by means ofelectro-dynamic loud-speakers, the combination with an electro dynamicloud speaker, of a sound box for'said loud speaker, a frame memberforming a wall of said box, a vibratory plate secured to said framemember, a light screen supporting said loud speaker in a manner to allowthe free vibration of the cone'or" said loud speaker and inclined withrespect to said plate.

4. In a mechanism for the electric amplification of sounds by means ofelectro-dynamic loudspeaker, the combination with an electro dynamicloud speaker, of a screen formed by a sounding board and supporting saidloud speaker in a manner to allow the free vibration of the cone of saidloud speaker.

JEAN KREssM NN.

